High throughout signal processors are required for many modern sensor, communication and control system applications. Said signal processors are often implemented as parallel or distributed combinations of several signal processing elements which are either identical or of a small number of types, in order to reduce the signal processor's design, fabrication or maintenance costs. Parallel or distributed implementations are also preferred for applications in which the total signal processing capacity required is not precisely known at the inception of design, or else is expected to change during the useful life of the equipment, due to modifications to the equipment or changes in the application. In these applications, signal processing elements may be added or deleted as needed to adjust the available signal processing capacity to the requirements of the application.
Prior art attempts to construct highly reliable self-repairing systems by the use of automatic substitution of spare system elements; however, the intricate switching networks or reconfiguration control hardware required to accomplish the spared element substitution, in addition to extensive checking circuitry, generally provide another source of single-point failures, thereby defeating the intended fault-tolerant goals. The use of switching and checking circuitry separate from the active system elements generally requires extensive redesign of the circuitry if system elements are later added or deleted, thereby defeating the intent of achieving a flexible system design through parallelism.
Other prior art attempts to achieve high system reliability have included triple or higher modular redundancy where each element is duplicated three or more times and a poll is taken among the elements. The majority vote among the plurality of elements is taken to be the correct output. These attempts lead to fault-free systems in which the failure of one element has no impact whatsoever on the performance of the system, and may be preferred for applications which require that the system make no errors over a relatively short period. The reliability of such systems diminishes over longer periods, however, when the probability of multiple element failures becomes significant. These attempts are particularly disadvantageous for applications which require only a self-repairing rather than a fault-free system, in that large numbers of extra components are required. These extra components increase both the initial cost of the system and the cost of maintaining the system; the additional size, weight and power required by said extra components are especially burdensome in airborne and space applications for fault-tolerant systems.